(1) Field of the Invention
The present invention relates to a procedure for facilitating the approach to a platform from an aircraft, and particularly from a short-landing aircraft such as an aircraft equipped, for example, with a rotary wing.
(2) Description of Related Art
Thus, the invention lies within the technical field of systems that provide assistance for the piloting of an aircraft, including, in particular, automated systems that aid the platform approach for rotary-wing aircraft.
In point of fact, a rotary-wing aircraft should be able to locate mobile platforms or vessels and to approach them safely, regardless of weather and visibility conditions, while avoiding any obstacles that may be present in the approach zone.
The approach is conducted by taking into consideration the direction and speed of the wind in the area; the type of platform to be approached (fixed platforms, mobile platforms, ships, or barges); any surrounding obstacles (cranes, barges, boats employed in the positioning of the platform, container vessels or supertankers navigating around the approach zone, or other surrounding platforms); and the comfort of the passengers.
Platform approaches typically consist of successive flight segments.
Accordingly, the approach includes an arrival segment that links the last flight point in the current flight phase and an initial approach point identified in English by the acronym “IAF” (Initial Approach Fix). This arrival segment is usually located at an altitude of 1,500 feet. It should be noted that the symbol “ft.” refers to the unit of length known in English as “feet,” each of which is equivalent to 30.48 centimeters.
An initial approach segment may link the initial approach fix (IAF) to an intermediate point identified in English by the acronym “IF” (Intermediate Fix). The purpose of this initial approach segment is to allow the aircraft to decelerate and to align itself along the trajectory to be followed.
An intermediate approach segment may link the intermediate fix (IF) to a final approach point identified in English by the acronym “FAF” (Final Approach Fix) in order to descend to an altitude that may be as low as 1,000 feet. The purpose of this segment is to align the aircraft, to decelerate, and to prepare for the final approach segment.
A final approach segment links the final approach fix (FAF) and a decision point identified in English by the acronym “MAP” (Missed Approach Point).
If the pilot establishes visual contact with the platform at the decision point, the pilot may land his aircraft on that platform.
Conversely, a segment known as a “go-around” must be performed if visual contact with the platform is not achieved at this stage in the approach. This go-around segment may also be performed at any time during the approach if the crew deems it appropriate. The purpose of this go-around segment is to return to a safe altitude.
The following documents contain known platform approaches:    The document designated as “AC90-80B” and entitled “Approval of Offshore Standard Approach Procedures, Airborne Radar Approaches, and Helicopter En Route Descent Areas”, published on Apr. 12, 1999;    JAR OPS 3, Section 2, Subpart E, IEM to Appendix 1 to JAR-OPS 3.430, sub-paragraph (d)” (Amendment 2, published on Jan. 1, 2002);    EU-OPS COMMISSION REGULATION (EU) No. 965/2012, of Oct. 5, 2012 (AMC1 CAT.OP.MPA.120 and GM1 CAT.OP.MPA.120); and    CAA paper No. 2010/01, entitled “The SBAS Offshore Approach Procedure (SOAP)”.
When weather conditions are unfavorable, an instrument approach is advantageous in terms of the stress imposed on the crew, who must manually pilot the aircraft in order to guide it to an area from which the platform can be acquired visually.
During the transition between the instrument-flight phase and the visual-flight phase, the crew must switch continuously between what is shown on the flight displays on the instrument panel and what can be observed through the windows in order to detect any indications and/or visual signs (such as lights or relief features) that allow the position of the platform to be confirmed. Therefore, this type of approach to platform is not the most practical one, and may sometimes give rise to errors of interpretation, for example, in the case of fog that causes a temporary loss of the visual acquisition of the landing target.
Up until now, the instrument approaches to a mobile platform or vessels have been conducted without the use of the navigation computer, identified in English by the acronym “FMS” (Flight Management System), and without a link to the autopilot of the aircraft on an approach trajectory predefined by the FMS.
Today, certain platforms are equipped with a device, identified in English by the acronym “NDB” (Non-Directional Beacon), which is used by the crew through the navigation computer as an aid to navigation and for the correlation of the position of the aircraft with relative precision. However, this resource does not allow for the construction of an approach flight plan.
A navigation computer is known that is used to provide horizontal guidance during the enroute phase. For the approach phase, the crew determines, as an aid to navigation, an off-route target point that corresponds to the coordinates of the platform to be reached. However, the navigation computer does not segment the various phases of the approach to the platform in order to slave the autopilot to these guidance data (e.g., the horizontal and vertical deviation, and the speed indication).
Therefore, the approach is conducted manually or semi-automatically, with the aid of certain higher autopilot modes, using the approach charts published by the operators and approved by the local authorities.
The aircraft's weather radar may also be used as a means for identifying the platform and for detecting and avoiding any temporary or stationary obstacles during the approach and the final descent.
Document US 2010/0168939 proposes a module and an automated procedure for an approach to a platform along an approach trajectory constructed from approach points.
According to this document US 2010/0168939, a pilot enters into a module on board the aircraft:                the coordinates of the target platform to be reached;        a final approach course toward the platform;        an offset distance that laterally separates the trajectory to be followed from a trajectory aimed at the platform according to this approach course; and        a descent height.        
Then, in response to the entered data, the module on board the aircraft determines, in particular, the position of the initial approach fix (IAF) and of the final approach fix (FAF). The aircraft is then guided toward the initial approach fix.
Thus, the constructed approach trajectory includes a horizontal segment that links an initial approach fix (IAF) and a final approach fix (FAF).
The trajectory then includes a descent segment followed by a level segment in order to link the final approach fix (FAF) to a decision point (MAP).
The initial approach fix (IAF), the final approach fix (FAF), and the decision point (MAP) are contained in a vertical plane that is parallel to the selected approach course. It should be understood that the term “vertical plane” refers to a plane that is oriented by weight, such that points on this vertical plane may be located at different altitudes.
This vertical plane is offset in relation to the platform by a distance equal to the offset distance that is entered.
This approach may entail the disadvantage of not being compatible with certain current procedures. In particular, it is not compatible with the ARA EU OPS approaches currently used in the North Sea.
Furthermore, this document does not take into consideration the specific characteristics of the platforms. In point of fact, the platforms have different shapes. Therefore, the specific location of a landing zone on a platform may not match the platform coordinates that were entered.
Document US 2008/0119970 relates to a precision approach guidance system that includes an inertial system, a terrain database, and an image sensor (or telemetry means).
The known technological background also includes the following documents:    Esterline CMC electronics, CMA-9000 Flight Management System Operator's Manual, Operational Program S/VV 169-614876-022, publication No. 9000-GEN-0105, Item No. 930-6000088-00 (Aug. 21, 2008);    N. McFarlane, A New Procedure for North Sea Helicopter Operations, Second GIANT User Forum (Brussels, Belgium; Oct. 9, 2008);    K. M. Dodson and J. R. A. Stevens, A North Sea Trial to Investigate the Use of Differential GPS for Instrument Approaches to Offshore Platforms (paper presented at the 23rd European Rotorcraft Forum (Dresden, Germany; September 1997);    U.S. Pat. No. 6,720,891; and    XP003032932, “EGNOS Offshore Helicopter Approach Procedure” (GIANT GNSS INTRODUCTION IN THE AVIATION SECTOR; Jan. 24, 2008).
Thus, the purpose of the present invention is to propose an approach procedure intended to assist a crew in landing on a platform with an aircraft.